The present invention relates to a process for reducing both the acidity and corrosivity of petroleum oils.
Whole crudes and crude fractions with high organic acid content such as those containing carboxylic acids, specifically naphthenic acids, are corrosive to the equipment used to extract, transport and process the crudes. Solutions to this problem have included use of corrosion-resistant alloys for equipment, use of corrosion inhibitors, and neutralization of the organic acids with various bases.
Efforts to minimize organic acid corrosion have included a number of approaches by neutralizing and removing the acids from the oil. For example. U.S. Pat. No. 2,302,281 and Kalichevsky and Kobe in Petroleum Refining with Chemicals (1956), Chapter 4, disclose various base treatments of oils and crude fractions. U.S. Pat. No. 4,199,440 discloses treatment of a liquid hydrocarbon with a dilute aqueous alkaline solution, specifically dilute aqueous NaOH or KOH. U.S. Pat. No. 5,683,626 teaches treatments of acidic crudes with tetra-alkylammonium hydroxide and U.S. Pat. No. 5,643,439 uses trialkylsilanolates. PCT US96/13688, US/13689 and US/13690 (Publication WO 97/08270, 97/08271 and 97/08275 dated Mar. 6, 1997) teach the use of Group IA and Group IIA oxides and hydroxides to treat whole crudes and crude fractions to decrease naphthenic acid content. U.S. Pat. No. 4,300,995 discloses the treatment of carbonaceous material, particularly coal and its products, heavy oils, vacuum gas oil, and petroleum resids having acidic functionalities with a dilute quaternary base, such as tetramethylammonium hydroxide in a liquid (alcohol or water). This patent was aimed at improving yields and physical characteristics of the products and did not address the question of acidity reduction.
It is known that mineral acids catalyze nucleophilic additions (esterification) of carboxylic acids with alcohols. (See, for example, Streitwieser, Jr. and Heathcock, Introduction to Organic Chemistry, second edition, Chapter 18, page 516.) However, the addition of such mineral acids to esterify organic acids in petroleum oils would be counterproductive since acid would be added to the oil to achieve an acid reduction. One would merely be replacing one acid with another, more corrosive acid.
While the above processes have achieved varying degrees of success there is a continuing need to develop more efficient methods for treating acidic crudes, particularly by decreasing the amounts of treating compounds used. Applicants"" invention addresses these needs.